This invention relates generally to a method and apparatus for monitoring the contact pressure being exerted when the printed image is being formed in a rotary printing press and more particularly to providing novel means to do so during press operation for any corrective action needed.
The contact pressure being exerted between rotating printing plates during operation of a rotary printing press, such as an offset printing press, a lithograph printing press and the like, is well recognized to undergo significant variation reducing the quality of the printed image. For example, too little contact pressure results in a printed image being faint or missing details and which can require the press operator to adjust the contact pressure during further press operation for avoidance of additional spoilage. Such corrective action taken by the press operator can understandably be carried out long after needed thereby causing considerable loss of the various objects on which the printed image is applied, such as metal cans, plastic containers and the like. In a similar manner, the application of excessive contact pressure when the printed image is being applied causes the liquid link to smear upon deposition and thereby require the press operator to make the necessary adjustments for reducing the amount of this operating factor during continued press operation. Such variation in contact pressure between the printing plates during operation of a rotary printing press can also be caused by a wide variety of operating conditions, including temperature changes, rotational speeds of operation, materials employed to produce the printed image and still other operating factors. A commonly experienced temperature change affecting contact pressure between the rotating printing plates occurs during press start-up after customary periods of press inactivity which causes critical printing surfaces to physical contract due to experiencing lower temperatures while being inactive. It remains desirable, therefore, to provide improved means whereby the printing contact pressure in a rotary printing press can be more effectively monitored during press operation.
Various methods and apparatus are already known to adjust the contact pressure between printing plate members of a rotary printing press. For example, there is disclosed in U.S. Pat. No. 5,181,468 a device to control the operating contact pressure between printing plate rollers of an offset printing press which includes employment of a pneumatic jack device to do so. The press operator is able to vary the operating pressure with such device during press operation. In U.S. Pat. No. 5,622,114 there is disclosed a method for adjusting contact between the printing plate rollers of a rotary printing press which first includes separating the rollers while stationary to permit a piezofilm to be inserted therebetween for generation of an output signal being transmitted to an optical image display device. In a different embodiment, a pneumatic device is employed for adjustment which can further include pressure sensor means connected to said optical display. Both methods are said to be useful xe2x80x9cas a partial solutionxe2x80x9d in enabling automated roller adjustment. An apparatus for such automated roller adjustment in a rotary printing press is also disclosed in U.S. Pat. No. 5,275,099. In doing so, the contact pressure between the rotating plate roller and a form roller physically abutting the rotating plate roller is detected with multiple strain gage sensors mounted on a mechanical pivoting arm. Correcting the contact pressure during press operation to a predetermined value is said to be achieved automatically with a feedback type servomechanism employing comparator means.
To overcome the aforesaid operational difficulties with such type rotary printing press, there is now provided a novel measurement system for monitoring the contact pressure between the printing plate rollers of a rotary printing press while being operated in a further improved manner. In the operation of the present measurement system, a continuous visual display of the dynamic variations occurring in the printing contact pressure during formation of the printed images enables the press operator to make more immediate corrections for any variations displayed beyond the control limits established for an acceptable printed image. In doing so, a display is first recorded on a visual screen, such as a PC monitor or other like device, for both customary upper and lower form roller contact pressure values so recorded when the particular printed image being formed is found acceptable to establish an envelope on the screen during continued press operation with respect to said printed image. A continuing display of said dynamic contact pressure values thereafter immediately notifies the press operator when any manual adjustment of the contact pressure controls is required to maintain said values within the previously recorded envelope appearing on the display screen. Providing a suitable continuous visual display in said manner can be carried out by sensing when a first printing plate disposed on the outer surface of a rotating plate roller of a rotary printing press comes into registration with a second printing plate disposed on the outer surface of a rotating blanket roller in said printing press, concurrently measuring the contact pressure being exerted between the customary pair of rotating form or inking rollers physically abutting the rotating plate roller during the time period when the printing plates on the plate roller and blanket roller remain in registration, further sensing the angular position of the rotating form rollers during the time period when the printing plates on the plate and blanket rollers remain in registration and continuously displaying the variation in contact pressure with respect to angular position of the rotating form rollers. A continuous monitoring of dynamic contact pressure values in this manner can understandably improve the operating efficiency of various type rotary printing presses to include those having single and multiple printing heads as well as those producing single and multicolored printed images.
It is an object of the present invention, therefore, to provide a monitoring system for operation of a rotary printing press to improve the visual quality of the printed image.
It is another object of the present invention to provide said presently improved monitoring system in a manner requiring only a relatively simple modification to the existing rotary printing press apparatus.
A still further object of the present invention is to provide a rotary printing press incorporating the presently improved monitoring system for increased operating efficiency.
It is yet another object of the present invention to provide a novel method for continuously monitoring the resulting quality of a printed image while being formed in a rotary printing press.
These and still further objects of the present invention will become apparent upon considering the following detailed description of the present invention.
It has now been discovered by the present applicant that a continuous visual monitoring system when carried out in a particularly defined manner can significantly improve the operating efficiency of a rotary printing press. Generally, the presently improved method for monitoring contact pressure between rotating printing plate members in said apparatus requires continuously sensing when a first printing plate disposed on the outer surface of a rotating plate roller in said printing press comes into registration with a second printing plate disposed on the outer surface of a rotating blanket roller in said printing press, concurrently measuring the contact pressure being exerted between a pair of rotating form rollers physically abutting the rotating plate roller during the time period when the printing plates on the plate roller and blanket roller remain in registration, further sensing the angular position of the rotating form rollers during the time period when the printing plates on the plate and blanket rollers remain in registration, and continuously displaying on a visual screen the variation in contact pressure with respect to angular position of the rotating form rollers that occurs during said time periods. In one embodiment wherein the contact pressure is monitored with a strain gage disposed at each end of both form rollers, it now becomes possible for the press operator to correct for variations occurring beyond previously established upper and lower limits being displayed on the visual screen with a greater degree of control. More particularly, multiple displays on the same visual screen can be employed enabling the press operator to continuously observe pressure fluctuations occurring over major areas of the printing surface such as horizontal as well as vertical and diagonal contact pressure variation.
A representative measurement system in accordance with the present invention comprises position sensing means to detect when a first printing plate disposed on the outer surface of a rotating plate roller in the rotary printing press comes into registration with a second printing plate disposed on the outer surface of a rotating blanket roller in the printing press, pressure sensing means to measure the contact pressure being exerted between a pair of form rollers physically abutting the rotating plate roller, rotational feedback means determining the angular position of the rotating form rollers during the time period when the printing plates on the plate and blanket rollers remain in registration, and visual display means continuously depicting the variation in contact pressure with respect to angular position of the rotating form rollers. In said embodiment, individual position sensing elements can be physically connected to the respective plate and blanket rollers in the conventional manner with a further operatively cooperating conventional encoder or resolver device being physically connected to the supporting shaft for the blanket roller. To increase the sensitivity of the contact pressure measurements being displayed in the present embodiment, an otherwise conventional strain gage device can be employed for attachment to each form roller in a further required manner. The multiple strain gage devices being employed for mounting on opposing ends of the central shaft supporting each form roller are affixed to the customary pivoting mechanical arm connected to each form roller and with each of said mechanical arms having been modified to include discontinuities or air gaps enabling greater flexure of the strain gage affixed thereto.
Incorporating the above illustrated monitoring system into an otherwise conventional rotary printing press of many types can be carried out in a routine manner. There is only further required well known analog and digital data processors, such as the Sigmeter data analyzer being sold by Sciemetric Company, Canada and still others having additional channel response for connection to the individual sensing devices being employed. The illustrated Sigmeter device acquires the strain gage voltages from both form rollers for conversion to a digital value. The changing digital values are then referenced in said device to the input encoder pulses being received for display as the ordinate of a conventional binary graph. The angular position values derived from the encoder or resolver device are also presented to the operationally connected visual display for the abscissa portion of said graph. In this manner, the envelope created with the upper form rollers forms one continuous display on said screen while the envelope for the lower form rollers is simultaneously displayed as a second envelope on said screen.